A negative air ion is an atom or molecule in the air that has gained an electron, while a positive ion has lost an electron. Both positive and negative ions occur naturally in the air. However, negative ions are more concentrated in fresh air. Negative air ions can be produced by lightning, ocean surf and waterfalls. There are also electrical devices called 'air ionisers' that produce negative air ions. Such air ionisers have been used in the treatment of seasonal winter depression, or seasonal affective disorder (SAD).
Levels of a chemical messenger in the brain called serotonin decrease in autumn and winter. This decrease may be related to the depression that some people experience in the winter months. It has been proposed that negative air ions cause an increase in brain serotonin levels.
There have been a number of well conducted studies which have looked at the effects of air ionisation on winter depression. Treatment generally involves sitting in a room with the ioniser on for 30 minutes every morning over a 2-3-week period. This type of treatment is effective in reducing depression symptoms in people with winter depression. Using a high-density ioniser is more effective than using a low-density ioniser.
There is less evidence on the use of negative air ionisation to treat non-seasonal depression, although current evidence is promising. One study used negative air ionisation to treat people with chronic major depression, and one study has used the treatment with university students (some of whom were depressed). Both studies found that negative air ionisation reduced depression symptoms. Again, a high-density ioniser was more effective than low-density one.
Air ionisers produce a very small amount of a gas called ozone, which can be harmful to humans. Air ionisers should be used in a well ventilated room to ensure that ozone levels do not build up to toxic levels.
Air ionizers are available from electronics stores and can be bought on the internet. It is important to check the technical specifications of any air ioniser. Some of those on sale do not produce a high density of negative ions. A high-density ioniser produces 2,700,000 ions per cubic centimeter, while a low-density one produces only 10,000 ions per cubic centimeter.
Air ionisation appears to be a promising treatment for seasonal winter depression. It also appears to be a promising treatment for general depression, but more research is needed to be sure it is effective.
Last reviewed and updated: 1 December 2016